Comb polymers having a halobutyl rubber backbone

ABSTRACT

The subject invention relates to comb polymers having a halobutyl rubber backbone and to techniques for synthesizing such polymers. The comb polymers of this invention can be thermoplastic elastomers. For instance, halobutyl rubbers having sidechains which are derived from vinyl aromatic monomers are thermoplastic elastomers which can be made by a technique of the subject invention. Such thermoplastic elastomers typically have a chlorobutyl rubber backbone and side chains which are comprised of polystyrene. The subject invention more specifically discloses a process for grafting a lithium terminated vinyl aromatic polymer onto a halobutyl rubber which comprises: (1) capping the lithium terminated vinyl aromatic polymer with a diene monomer to produce a lithium terminated diene capped vinyl aromatic polymer, and (2) reacting the lithium terminated diene capped vinyl aromatic polymer with the halobutyl rubber to produce a halobutyl rubber having vinyl aromatic sidechains grafted thereto.

This is a divisional of application Ser. No. 07/498,676 filed on Mar.26, 1990, now abandoned.

BACKGROUND OF THE INVENTION

There are many potential uses for graft polymers having halobutyl rubberbackbones. For instance, chlorobutyl rubber which has low airpermeability and outstanding age resistance is incompatible with mostrubbers commonly utilized in building tires. Chlorobutyl rubber isaccordingly a highly desirable rubber for incorporation into tirecompounds but is very difficult to cocure with other rubbers utilized inthe tire compound. By grafting a polydiene rubber, such a polybutadiene,onto chlorobutyl rubber, the chlorobutyl rubber is compatibilized withmost common rubbers utilized in building tires and can be veryeffectively cocured therewith.

Heretofore, it has been very difficult, if not impossible, to synthesizegraft polymers having halobutyl rubber backbones. Prior attempts tograft polystyryl lithium onto chlorobutyl rubber have all resulted infailure. Prior to the subject invention, attempts to graft sidechainswhich are derived from diene monomers onto halobutyl rubber backboneshave also resulted in enormous difficulties.

SUMMARY OF THE INVENTION

By practicing the techniques of this invention, vinyl aromaticsidechains and/or sidechains derived from diene monomers can be graftedonto halobutyl rubbers. For instance, sidechains which are derived fromstyrene can be grafted onto chlorobutyl rubber. Such graft polymershaving polystyrene sidechains and a backbone which is comprised ofchlorobutyl rubber are thermoplastic elastomers. These thermoplasticelastomers are highly useful in a wide variety of applications. Thechlorobutyl rubber backbone provides these polymers with outstanding ageresistance. Because chlorobutyl rubber and polystyrene are relativelyinexpensive, graft polymers of this type can be prepared at only afraction of the cost of conventional ABA-block thermoplastic elastomers.Such graft copolymers having chlorobutyl rubber backbones andpolystyrene sidechains can also be blended with polyphenylene oxide tomake very high performance blends.

The subject invention specifically discloses a process for grafting alithium terminated vinyl aromatic polymer onto a halobutyl rubber whichcomprises: (1) capping the lithium terminated vinyl aromatic polymerwith a diene monomer to produce a lithium terminated diene capped vinylaromatic polymer, and (2) reacting the lithium terminated diene cappedvinyl aromatic polymer with the halobutyl rubber to produce a halobutylrubber having vinyl aromatic sidechains grafted thereto. Thus, bypracticing the process of the subject invention, it is possible to makea thermoplastic elastomer which is comprised of a halobutyl rubberhaving sidechains grafted thereto, where said sidechains are derivedfrom at least one vinyl aromatic monomer.

The present invention also reveals an elastomeric polymer which iscomprised of a halobutyl rubber having sidechains grafted thereto,wherein said sidechains are derived from at least one diene monomer. Forexample, the present invention provides a process for preparing anelastomeric polymer having a halobutyl rubber backbone and3,4-polyisoprene sidechains, said process being comprised of reacting ahalobutyl rubber with lithium terminated 3,4-polyisoprene, wherein saidlithium terminated 3,4-polyisoprene was made by the polymerization ofisoprene monomer in the presence of tripiperidino phosphine oxide as amodifier. Typical polyisoprene rubbers synthesized with lithiuminitiators having cis-isomer contents of 60% to 85% can also be graftedto halobutyl rubbers.

The subject invention also provides a process for preparing anelastomeric polymer having a halobutyl rubber backbone and highvinyl-polybutadiene or medium vinyl polybutadiene sidechains, saidprocess being comprised of reacting a halobutyl rubber with lithiumterminated high vinyl polybutadiene or medium vinyl polybutadiene,wherein the lithium terminated polybutadiene was made by thepolymerization of 1,3-butadiene monomer in the presence of potassiumt-amylate as a modifier at a temperature of less than about 25° C.

High vinyl polybutadiene normally has a vinyl content of greater than65%. Medium vinyl polybutadiene has a vinyl content of 35% to 60%.Unmodified lithium polybutadiene has a vinyl content of less than about15%. In most cases unmodified polybutadiene made utilizing a lithiuminitiator has a vinyl content which is within the range of about 8% toabout 10%. Unmodified lithium polybutadiene will also readily react withhalobutyl rubbers to produce graft polymers having halobutyl rubberbackbones and unmodified polybutadiene sidechains. Unmodified lithiumpolyisoprene and lithium styrene-butadiene rubber (SBR) also readilyreact with halobutyl rubber to make comb polymers.

DETAILED DESCRIPTION OF THE INVENTION

A halobutyl (halogenated butyl) rubber is utilized as the backbone inthe graft, polymers of this invention. Butyl rubbers are made by thecopolymerization of isobutylene monomer with a small quantity ofisoprene monomer. Butyl rubber is accordingly comprised of repeat unitswhich are derived from isobutylene and isoprene. Such butyl rubbertypically contains from about 0.5% to about 5% by weight isoprene andfrom about 95% by weight to about 99.5% by weight isobutylene. Butylrubbers more typically contain from about 1 to about 3 weight percentisoprene and from about 97% to about 99% isobutylene. The halogenatedbutyl rubbers utilized in accordance with this invention are prepared byhalogenating such butyl rubbers. A molar ratio of the halogen to doublebonds in the butyl rubber of approximately 1:1 is typically utilized insuch halogenation procedures. Halobutyl rubbers can be prepared byhalogenating butyl rubber with any halogen. In most cases, the butylrubber will be halogenated with fluorine, chlorine or bromine.

In the practice of this invention chlorobutyl rubbers and bromobutylrubbers will typically be utilized. These halobutyl rubbers willnormally have a number average molecular weight which is within therange of about 100,000 to about 500,000. In most cases, it is preferredto utilize a halobutyl rubber having a molecular weight which is withinthe range of about 300,000 to about 350,000. Such halobutyl rubbers willtypically contain from about 50 to about 100 halogen atoms per polymerchain in the rubber. In most cases, the halobutyl rubber will containfrom about 0.5 to about 5 weight percent of the halogen. In most cases,it is preferred for the halobutyl rubber to contain from about 0.75 toabout 3 weight percent of the halogen. It is typically most preferredfor the halobutyl rubber to contain from about 1% to about 2% of thehalogen. Such halobutyl rubbers are commercially available from ExxonChemical Company and Polysar Limited. Such representative examples ofcommercially available halobutyl rubbers which can be employed include:Exxon Chlorobutyl 1065, Exxon Chlorobutyl 1066, exxon Chlorobutyl 1068,Polysar Chlorbutyl 1240, Polysar Chlorobutyl 1255, Exxon Bromobutyl2222, Exxon Bromobutyl 2233, Exxon Bromobutyl 2244, Exxon Bromobutyl2255, Polysar Bromobutyl X2, and Polysar Bromobutyl 2030.

The grafting procedure required varies with the type of sidechain beinggrafted onto the halobutyl rubber. In other words, the conditionsrequired for the grafting procedure will vary with the type of sidechainbeing grafted onto the halobutyl rubber.

In cases where vinyl aromatic polymers are grafted onto halobutylrubbers, a very special procedure must be employed. In this procedure,the vinyl aromatic polymer must be capped with a diene monomer before itis grafted onto the halobutyl rubber. Such diene monomer capped vinylaromatic polymers can be prepared by simply adding a small amount ofdiene monomer to a solution of living lithium terminated polystyrene. Itis only necessary to utilize enough of the diene monomer to cause theorange (styryl) color of the living lithium terminated polystyrenesolution to disappear. It is believed that it is only necessary for thepolystyrene chain to be capped with 1 diene monomer. Of course, greaterquantities of the diene monomer can be utilized. However, there is notbelieved to be any advantage associated with the utilization of excessquantities of diene monomer. Any diene monomer can be utilized in thecapping procedure. However, in most cases 1,3-butadiene or isoprene willbe utilized. This capping reaction proceeds very rapidly at roomtemperature.

In the capping procedure living lithium terminated polystyrene is cappedwith a diene monomer to produce a lithium terminated diene capped vinylaromatic polymer. This reaction can be depicted as follows: ##STR1##wherein P illustrates the polymer chain.

In the reaction depicted lithium terminated polystyrene chains reactwith 1,3-butadiene monomer to produce a lithium terminated butadienecapped polystyrene. The capping reaction is typically carried out in aninert organic solvent, such as cyclohexane, hexane, benzene or toluene.It is normally advantageous for the capping procedure to be carried outunder an inert atmosphere, such as nitrogen.

A wide variety of vinyl aromatic polymers can be grafted onto halobutylrubbers utilizing the technique of this invention. For example,polystyrene, vinyl toluene, p-methylstyrene, and α-methylstyrene can begrafted onto halobutyl rubbers to make useful thermoplastic elastomers.These vinyl aromatic polymers will typically have number averagemolecular weights which are within the range of about 500 to about500,000. More typically, the vinyl aromatic polymers will have molecularweights which are within the range of about 1,000 to about 100,000. Itis normally preferred for the vinyl aromatic polymer to have a numberaverage molecular weight which is within the range of about 3,000 toabout 40,000. These lithium terminated vinyl aromatic polymers can bemade utilizing standard procedures which are well known to those skilledin the art. They are typically made by the solution polymerization ofstyrene monomer with a lithium catalyst being employed. A wide varietyof lithium catalysts can be employed.

The lithium catalysts which can be used are typically organolithiumcompounds. Organo monolithium compounds, such as alkyllithium compoundsand aryllithium compounds, are usually employed. Some representativeexamples of organo monolithium compounds that can be utilized includeethyllithium, isopropyllithium, n-butyllithium, secondary-butyllithium,normal-hexyllithium, tertiary-octyllithium, phenyllithium,2-napthyllithium, 4-butylphenyllithium, 4-phenybutyllithium,cyclohexyllithium and the like. Normal-butyllithium andsecondary-butyllithium are highly preferred lithium catalysts.

The amount of lithium catalyst utilized will vary from one organolithiumcompound to another and with the molecular weight that is desired forthe polystyrene being synthesized. As a general rule, from about 0.01phm (parts per hundred parts by weight of monomer) to 1 phm of thelithium catalyst will be employed. In most cases, from 0.01 phm to 0.1phm of the lithium catalyst will be employed with it being preferred toutilize 0.025 phm to 0.07 phm of the lithium catalyst.

The lithium terminated diene capped vinyl aromatic polymer will readilyreact with the halobutyl rubber. It is important to add the solution ofthe lithium terminated diene capped vinyl aromatic polymer to a solutionof the halobutyl rubber. It is not desirable to revert this order ofaddition because the first halobutyl rubber added to the solution oflithium terminated diene capped vinyl aromatic polymer would be veryhighly grafted with the rubber added subsequently being only verylightly grafted.

The temperature at which this grafting procedure is carried out is notparticularly critical. In fact, the grafting reaction proceeds veryrapidly at room temperature (about 18° C. to about 26° C.). However, inthe case of α-methylstyrene containing vinyl aromatic polymers, it isimportant to maintain a temperature below about 60° C. This is importantbecause α-methylstyrene polymers can rapidly depolymerize attemperatures above about 60° C.

The solution of halobutyl rubber will normally be scavenged with anorganolithium compound before the grafting procedure is carried out toprevent gelation. The halobutyl rubber solution will typically bescavenged with a very dilute solution of a normal alkyllithium compound.Normal-butyllithium is preferred as a scavenger. Secondary-butyllithiumdoes not yield satisfactory results. The normal-alkyllithium solutionemployed will typically contain 5 weight percent n-alkyllithium or lessbased upon the total weight of the solution. In most cases from about0.5 to about 3% n-alkyllithium will be in the scavenger solution. It istypically preferred for the scavenger solution to contain from about 1to about 2% of the n-alkyllithium compound. In the case of a 10%halobutyl rubber cement, about 10 ml of the n-alkyllithium solution willbe needed for 100 ml of the halobutyl rubber cement. The halobutylrubber cement will typically have a solids content which is within therange of about 2 to about 30 weight percent. It is normally preferredfor the halobutyl rubber solution to contain from about 5 to about 20weight percent of the halobutyl rubber. It is normally most preferredfor the halobutyl rubber cement to contain from about 10 to about 15weight percent of the halobutyl rubber.

To produce a graft polymer which is a thermoplastic elastomer, it willtypically be necessary to incorporate from about 10 to about 40 weightpercent of the vinyl aromatic polymer into the graft polymer. In mostcases, it is preferred to incorporate from about 15 weight percent toabout 35 weight percent of the vinyl aromatic polymer into the graftpolymer.

The graft copolymers of this invention having halobutyl rubber backbonesand vinyl aromatic sidechains can be blended with polyphenylene oxide toimprove the impact strength thereof. Polyphenylene oxide is a widelyused engineering plastic having a very high surface temperature. Withoutmodification, polyphenylene oxide melts at about 250° C. and isextremely brittle. The very high temperature required to processpolyphenylene oxide can be reduced by blending it with polystyrene sinceboth of these polymers exhibit the unusual feature of being fullysoluble in each other at any ratio. Unfortunately, such blends ofpolyphenylene oxide and polystyrene are also brittle, since both ofthese polymers are brittle by themselves. However, when the graftpolymers of this invention having halobutyl rubber backbones andpolystyrene sidechains are mixed with polyphenylene oxide, a matrix isformed wherein the brittle polyphenylene oxide-polystyrene domains arelinked with elastomeric halobutyl rubber segments. Such blends exhibitthe properties of tough, reinforced engineering plastics. The amount ofgraft copolymers utilized in such blends will typically be adequate togive the overall blend a halobutyl rubber content which is within therange of about 4 to about 25 weight percent. Such blends will moretypically contain from about 6 to about 15 weight percent halobutylrubber based upon the total weight of the blend. The graft copolymersutilized in such blends can be thermoplastic elastomers ornonelastomeric (hard) plastics.

Halobutyl rubbers provide low air permeability and outstanding ageresistance. These are characteristics which are often sought in tirerubbers. However, the addition of halobutyl rubbers to most standarddiene rubbers, such as polyisoprene and polybutadiene, by conventionaltechniques yields blends which exhibit improved age resistance, butwhich are deficient in flex, tear, tensile strength and adhesion toother higher components. Thus, it has not been possible to achieve thedesired characteristics of halobutyl rubbers by simply blending theminto standard tire compounds.

By utilizing the techniques of this invention, it is possible to graftpolydiene rubber sidechains onto halobutyl rubbers. The elastomericgraft polymers which result can be blended into standard tire rubbercompounds to attain improved air permeability and age resistance withoutsacrificing flex, tear, tensile strength or adhesion to other tirecomponents. Additionally, such blends exhibit good cocurability and canbe utilized in building tires which display improved traction androlling resistance.

Lithium terminated 3,4-polyisoprene can be grafted onto halobutylrubber. It is important for the 3,4-polyisoprene to be synthesized bythe polymerization of isoprene utilizing a lithium catalyst. This willresult in the 3,4-polyisoprene being lithium terminated. It is alsoimportant for the 3,4-polyisoprene to be synthesized in the presence oftripiperidionophosphine oxide as a modifier. The lithium terminated3,4-polyisoprene made by the polymerization of isoprene in the presenceof tripiperidinophosphine oxide can be readily grafted onto halobutylrubbers by simply mixing a solution of the lithium terminated3,4-polyisoprene into a solution containing the halobutyl rubber. Thisgrafting reaction occurs very rapidly at ambient temperature.

High vinyl polybutadiene and medium vinyl polybutadiene sidechains canalso be grafted onto halobutyl rubber utilizing the techniques of thisinvention. The high vinyl polybutadiene or medium vinyl polybutadieneutilized will be lithium terminated. It is accordingly synthesized witha lithium catalyst. In the case of high vinyl polybutadiene and mediumvinyl polybutadiene, it is important to utilize potassium t-amylate asthe modifier. Accordingly, the high vinyl polybutadiene or medium vinylpolybutadiene will be prepared by the polymerization of 1,3-butadienemonomer in the presence of potassium t-amylate. It is also important toprepare the high vinyl polybutadiene or medium vinyl polybutadiene at apolymerization temperature or less than about 35° C. The polymerizationtemperature employed will normally be within the range of about -10° C.to about 90° C. with temperatures in the range of about 10° C. to 20° C.being preferred. The lithium terminated high vinyl polybutadiene orlithium terminated medium vinyl polybutadiene can readily be graftedonto halobutyl rubbers. This grafting procedure can be carried out bysimply mixing a solution containing the high vinyl polybutadiene ormedium vinyl polybutadiene into a solution containing the halobutylrubber. This grafting reaction occurs very rapidly at room temperature.

Unmodified polybutadiene synthesized with a lithium initiator can alsobe grafted onto halobutyl rubbers utilizing the techniques of thisinvention. This type of grafting results in the formation of combpolymers having halobutyl rubber backbones and unmodified polybutadienesidechains which have vinyl contents of less than 15%. Such a graftingprocedure can be carried out by simply mixing a solution containing theunmodified polybutadiene into a solution containing the halobutylrubber. Unmodified polyisoprene made with a lithium initiator and SBRmade with a lithium initiator can also be grafted onto halobutyl rubbersto make comb polymers.

This invention is illustrated by the following examples which are merelyfor the purpose of illustration and are not to be regarded as limitingthe scope of the invention or the manner in which it can be practiced.Unless specifically indicated otherwise, all parts and percentages aregiven by weight.

EXAMPLE 1

In this experiment a thermoplastic elastomer having a chlorobutyl rubberbackbone and polystyrene sidechains was prepared. In the procedureutilized, a solution containing 700 ml of cyclohexane and 100 ml ofstyrene was passed through silica and charged into a quart (946 ml)polymerization bottle under nitrogen. Then, 2.5 ml of a 1.25M solutionof s-butyllithium was added to initiate the polymerization which wascarried out at a temperature of 50° C. for three hours. This resulted inthe synthesis of lithium terminated polystyrene. The lithium terminatedpolystyrene was capped with butadiene upon cooling by adding 20 ml of a15% solution of 1,3-butadiene in hexane. After the 1,3-butadienesolution was injected into the polystyrene solution, the orange coloredcement turned bright yellow. Thus, enough butadiene was added to causethe orange (styryl) color to disappear.

The solution of the lithium terminated butadiene capped polystyrene wassubsequently added to 1.5 liters of 20 weight percent solution ofchlorobutyl rubber in cyclohexane. This addition was done under anitrogen atmosphere. The chlorobutyl rubber cement was previouslyscavenged with 150 ml of a 0.1M lithiumoligobutadiene (molecular weightless than about 1000) solution. To carry out this grafting procedure,solubility is extremely important. If the combined cements are not fullysoluble in each other, then the extent of grafting will be extremelylimited. Using cyclohexane as the solvent for the polystyrene issatisfactory. Cyclohexne is a preferred solvent for the chlorobutylrubber. Hexane may also be utilized as the solvent for the chlorobutylrubber, but toluene should be added to increase overall solubility.

Utilizing the same general procedure, a series of graft polymers havingchlorobutyl rubber backbones and polystyrene sidechains weresynthesized. The series of polymers synthesized in this series ofexperiments and their properties are described in Table I. A series ofgraft polymers having a ratio of chlorobutyl rubber to polystyrene of38:62 was prepared. The polystyrene utilized in making these graftpolymers had molecular weights ranging from about 10,000 to about500,000. The graft polymers prepared varied on the average number ofsidechains from less than 1 to 24. At 10,000 (24 teeth), the polymer wasrigid but clear. The polymers became flexible at 28,000 (8 teeth) andwere extremely hard at 100,000 (2.4 teeth). The polymers softened atmolecular weights of 150,000 and higher (2 or less teeth).

In the next series of experiments, graft polymers having a ratio ofchlorobutyl rubber to polystyrene of 60:40 were prepared. Startlingresults were observed in this series of experiments. In cases where themolecular weight of the polystyrene sidechains was 12,000 (16 teeth),the polymer was clear, with some stiffness. As the molecular weight ofthe polystyrene sidechains was increased to 28,000 (7 teeth), thepolymer became rubbery and self-reinforcing. This observation wasextremely surprising because even though it was recognized that equalmolecular weight polystyrene grafts could fulfill the role of the hardblocks in ABA-type thermoplastic elastomers, there is no control overthe length of the soft segments between the hard segments as is requiredin ABA-type thermoplastic elastomers. In fact, the actual distributionof the isoprene units with its allylic chlorine groups along the butylrubber chain is not known. All that is known is that the averagechlorobutyl rubber molecule has a molecular weight of approximately350,000 with about 80 to 100 allylic chlorine atoms, which puts theaverage segment of polymer between 2 chlorine atoms around 3,500molecular weight (assuming an even distribution).

Following the discovery of self-reinforcement, the range of thisphenomena was explored. The window of self-reinforcement turned out tobe quite large. The chlorobutyl rubber/polystyrene ratio extendsapproximately from 90:10 to 60:40 with the polystyrene teeth molecularweight ranging from about 5,000 to about 40,000, and the number of teeth(sidechains) ranging from 3 to about 30.

                                      TABLE I                                     __________________________________________________________________________    Comb Structured Graft Polymers with Chlorobutyl Rubber Backbones and          Polystyrene Sidechains                                                        (Teeth) with CB/PS Ratios from 38/62 to 88/12 and Sidechain Molecular         Weights of 10,000 to                                                          500,000. Tensile strips were cast from CH.sub.2 Cl.sub.2 Solution                          Approx.         % of Grafted                                                                              Elon-                                Chlorobutyl/                                                                         Teeth # of       Appear-                                                                            Phase  Tensile                                                                            gation                                                                            Modulus                                                                             Modulus                    Polystyrene                                                                          M Wt. Teeth                                                                              Rigidity                                                                            ance by GPC Strength                                                                           %   % Yield                                                                             100%                                                                              300%                                                                              500%               __________________________________________________________________________    38/62  10,000                                                                              24   Rigid Almost                                                                             77                                                                       Clear                                                 38/62  28,000                                                                              8    Flexible                                                                            Cloudy                                                                             84                                               38/62  29,000                                                                              8    Flexible                                                                            Cloudy                                                                             79                                               38/62  38,000                                                                              7    Flexible                                                                            Cloudy                                                                             73                                               38/62  100,000                                                                             2    Hard  Cloudy                                                                             57                                                                 Plastic                                                     38/62  150,000                                                                             2    Leather                                                                             Cloudy                                                                             55                                                                 Like                                                        38/62  300,000                                                                             1    Leather                                                                             Cloudy                                                                             --                                                                 Like                                                        38/62  500,000                                                                             1    Leather                                                                             Cloudy                                                                             --                                                                 Like                                                        60/40  12,000                                                                              16   Some  Clear                                                                              86.5   2027 700 730   559 802 1324                                 Stiffness                                                   60/40  28,000                                                                              7          Clear                                                                              80.1   1725 710 550   450 707 1107               60/40  40,000                                                                              5-6  V Strong                                                                            Hazy 85     1566 670 605   454 704 1072               60/40  64,000                                                                              3    V Strong                                                                            Sl   75     1482 710 647   565 735 1112                                 Soft  Cloudy                                                60/40  75,000                                                                              2.5  Snappy                                                                              Cloudy                                                                             63                                               60/40  100,000                                                                             2    Some  Cloudy                                                                             54                                                                 Strength                                                    60/40  150,000                                                                             1.3  Soft  Cloudy                                                                             49                                                                 No                                                                            Strength                                                    70/30   4,000                                                                              32              74.5   1603 890 160   224 462 744                70/30   6,000                                                                              21   Some  Sl Haze                                                                            88     1973 870 479   349 575 918                                  Stiffness                                                   70/30  15,000                                                                              8.5  V Strong                                                                            Cloudy                                                                             50     1784 1020                                                                              151   165 309 540                70/30  26,000                                                                              5    V Strong                                                                            Clear                                                                              86     1669 830 388   295 518 842                75/25  15,000                                                                              6-7  V Strong                                                                            Hazy 80                                               80/20  25,000                                                                              2.4        Cloudy                                                                             85.8   1168 1092                                                                               77   161 265 431                78/22  12,000                                                                              7          Clear                                                                              84.7   1620 1020                                                                              109   131 255 431                78/22   6,000                                                                              14         Clear                                                                              84.1   1681 1020                                                                              111   151 313 465                88/12   6,000                                                                              7          Clear                                                                              95     1930 390 552   498 1030                                                                               0                 88/12  12,000                                                                              3.5        Hazy 96     1750 1180                                                                               0     54 128 230                __________________________________________________________________________

The graft polymers exhibiting self-reinforcing characteristics weredissolved in methylene chloride and films were cast from them onstretched cellophane. After allowing several days for drying, thestress-strain properties reported in Table I were determined. Thestress-strain characteristics of these polymers compare very favorablywith those of Kraton™ G 1650, a commercially available hydrogenatedstyrene-polydiene block copolymer, which was evaluated for purposes ofcomparison. The best tensile strength of the graft copolymers made isvery comparable to that of the Kraton™ control. However, the graftpolymer made has an elongation which was approximately twice that of thestyrene-polydiene block copolymer.

EXAMPLE 2

In this experiment graft polymers having chlorobutyl rubber backbonesand polystyrene sidechains were blended with polyphenylene oxide. In theprocedure utilized, 184.5 grams of polyphenylene oxide was mixed with65.75 g of the graft polymer in a Brabender mixer above the flexingtemperature. The hard plastic was cut with a band saw into pieces nolonger than 1 inch (2.54 cm) and ground in a grinder with excess dry iceto increase brittleness. The powder obtained was subsequently moldedinto 0.25 inch (6.35 mm) sheet from which half inch (12.7 mm) stripswere cut with a band saw. The strips were then tested for izod impactstrength utilizing ASTM Test Procedure D 256-56 (1961).

A series of blends were prepared utilizing the graft polymers describedin Example 1 having a ratio of chlorobutyl rubber to polystyrene of38:62. These graft polymers had polystyrene segment molecular weightsranging from 10,000 to 300,00. The number of polystyrene sidechains inthese polymers varied from less than 1 to about 24. The level of graftpolymer utilized in the blends was chosen so as to give an overallrubber content of about 10%. In other words, about 10% of the overallweight of the blend was attributable to the chlorobutyl rubber in thegraft polymer with about 90% of the overall weight of the blend beingattributable to the polystyrene sidechains in the graft copolymer andthe polyphenylene oxide. As a control, unblended polyphenylene oxide wastested for izod impact strength. A modified polyphenylene oxideengineering plastic (Noryl EN 265) was also tested for izod impactstrength for purposes of comparison. Noryl EN 265 is a commerciallyavailable engineering plastic which is widely sued in manufacturinghousings for computers and other business equipment.

The data obtained and reported in Table II shows that the izod impactstrength of polyphenylene oxide is very poor. The impact strength of thecommercially available modified polyphenylene oxide is much better.However, even higher impact strength can be realized by blendingpolyphenylene oxide with the graft polymers of tis invention.

                                      TABLE II                                    __________________________________________________________________________    Impact Strength of Various Blends of Chlorobutyl Rubber/                      Polystyrene Graft Polymers with Polyphenylene Oxide                                          Izod Impact Data                                                                        Foot Lbs.                                                           Gauge                                                                              Inch per Inch                                                            (Inches)                                                                           Lbs. of Face                                                                             Average                                        __________________________________________________________________________    Controls                                                                      Noryl EN-265   .235 .800 3.40                                                                .229 .875 3.83                                                                .231 .750 3.24  1.5                                                           .230 .850 3.70                                                                .232 .775 3.34                                                 Polyphenylene  .249 .475 1.90                                                 Oxide (unblended)                                                                            .247 .400 1.62                                                                .249 .375 1.50  1.49                                                          .250 .200 .80                                                                 .247 .400 1.62                                                 Graft Polymers                                                                Approx.                                                                            Approx.                                                                            %                                                                   "Teeth"                                                                            # of Grafted                                                             M Wt "Teeth"                                                                            Phase                                                               38,000                                                                             7    73   .233 .825 3.54                                                                .233 .700 3.00                                                                .231 1.375                                                                              5.95  4.09                                                          .230 1.000                                                                              4.34                                                                .234 .850 3.63                                                 28,000                                                                             8    84   .240 .875 3.64                                                                .235 1.10 4.68*                                                               .234 1.000                                                                              4.27  4.65                                                          .241 1.750                                                                              7.26*                                                               .229 .775 3.38                                                 29,000                                                                             8    79   .244 .800 3.28                                                                .240 .775 3.22                                                                .234 .500 2.14  2.90                                                          .237 .775 2.84                                                                .241 .725 3.00                                                 10,000                                                                             24   77   .241 .675 2.80                                                                .236 .700 2.96                                                                .249 .650 2.61  2.62                                                          .231 .600 2.60                                                                .236 .550 2.33                                                 100,000                                                                            2.4  57   .231 .550 2.38                                                                .229 .700 3.06                                                                .229 .700 3.06                                                                .228 .725 3.18                                                                .231 .700 3.03                                                 150,000                                                                            2    55   .232 .400 1.72                                                                .231 .350 1.52                                                                .236 .250 1.06  1.50                                                          .238 .400 1.68                                                 __________________________________________________________________________

As can be seen by reviewing Table II, the highest impact strength (notaverage) attained was 7.26 foot pounds per inch of face which is almosttwice the best value achieved utilizing Noryl EN 265. Since in thesesample preparations, optimum conditions were not likely to be achieved,due to lack of proper mixing and molding equipment, maximum readings maybe more significant than statistical averages. Moreover, the fact thatthe two highest readings on the sample did not break completely, butheld together after the break (hinge break) also indicate that they weresuperior to the other examples which broke completely. The reinforcingpower of the grafted comb polymers was highest when the sidechains had amolecular weight of about 28,000 (8 polystyrene teeth per chlorobutylrubber molecule) and 84% grafted phase level. With higher polystyreneteeth molecular weights (150,000) and fewer teeth and lower graftingefficiency (grafted phase 55%), impact strength of the blend wasequivalent to unmodified polyphenylene oxide.

EXAMPLE 3

In this experiment, a comb polymer having a chlorobutyl rubber backboneand medium vinyl polybutadiene sidechains was prepared. In the procedureused, 750 ml of a premix solution containing 15%, 1,3-butadiene inhexane was charged into a quart (946 ml) polymerization bottle undernitrogen. As a modifier, 0.75 ml of a 1.1M solution potassium t-amylatewas added. Tehn, 1.75 ml of a 1.3M solution of secondary-butyl lithiumin hexane was added to initiate the polymerization. The polymerizationwas carried out at a temperature of about 15° C. for about 4 hours. Fullconversion was confirmed by solids measurement. The molar ratio of thesecondary-butyl lithium initiator to the potassium t-amylate was 0.27.However, in such polymerizations medium vinyl polybutadiene can be madeutilizing any molar ratio of the lithium initiator to potassiumt-amylate which is within the range of about 0.1:1 to about 1:1. In mostcases, the medium vinyl bolybutadiene will be synthesized using a molarratio of lithium initiator to potassium t-amylate which is within therange of about 0.15 to about 0.60. The solution of the medium vinylpolybutadiene was added to 750 ml of a chlorobutyl rubber solution whichcontained 100 g of polymer per liter of hexane. The chlorobutyl rubbercement was previously scavenged under nitrogen with 7.5 ml of a 1.6Msolution of n-butyllithium which was diluted with 75 ml of hexane. GPCconfirmed that the grafting reaction of this experiment was virtuallyquantitative.

EXAMPLE 4

A comb polymer having a chlorobutyl rubber backbone and 3,4-polyisoprenesidechains was made in this experiment. In the procedure employed, 625ml of hexane, 110 g of isoprene, 4 ml of a 1.3M solution ofsecondary-butyl lithium in hexane, and 8.75 ml of a 0.2M solution oftripiperidinophosphine oxide in hexane were charged into a quart (946ml) bottle. The polymerization was carried out at a temperature of 15°C. for about 4 hours. Full conversion was confirmed by solidsmeasurement. The molar ratio of secondary butyl lithium totripiperidinophosphine oxide employed in this experiment was 0.3.However 3,4-polyisoprene can be made utilizing any molar ratio oflithium initiator to tripiperidinophosphine oxide which is within therange of about 0.15:1 to about 0.60:1. The grafting was carried out asdescribed in Example 3. GPC showed that a very high degree of graftingwas attained.

EXAMPLE 5

In this experiment a graft polymer having a chlorobutyl rubber backboneand SBR sidechains was prepared. In the procedure employed, 750 ml of apremix solution containing 15% butadiene in hexane, 17 g of styrene, 4ml of a 1.3M solution of secondary-butyl lithium in hexane, and 0.75 mlof a 1.1M solution of potassium t-amylate in hexane were charged into aquart (946 ml) polymerization bottle. The polymerization was carried outat a temperature of 45° C. for about 4 hours. Full conversion wasconfirmed by solids measurement. In this experiment, the molar ratio ofthe secondary-butyllithium initiator to potassium t-amylate was 0.6.However, in making SBR any molar ratio of the lithium initiator topotassium t-amylate which is within the range of about 0.2:1 to about1.4:1 can be employed. The polymerization temperature utilized in makingsuch SBR can range from about -10° C. to about 90° C. Temperatures ofabout 20° C. to about 70° C. are generally preferred.

The grafting was carried out as described in Example 3. GPC analysisshowed that the grafting reaction was essentially quantitative. Afteremploying the grafting techniques of this invention, it is oftenimpossible to detect the presence of lithium polymer precursers. Lowerlevels of grafting may, of course, be attained by reducing the scavengelevel. However, in most cases, it will be desirable to achieve a highlevel of grafting.

While certain representative embodiments and details have been shown forthe purpose of illustrating the present invention, it will be apparentto those skilled in his art that various changes and modifications canbe made therein without departing from the scope of the presentinvention.

What is claimed is:
 1. An elastomeric polymer having low airpermeability and outstanding age resistance which can be blended withstandard tire compounds while maintaining satisfactory flex, tear andtensile strength which is comprised of a halobutyl rubber having anumber average molecular weight which is within the range of about100,000 to about 500,000 selected from the group consisting ofbromobutyl rubbers and chlorobutyl rubbers wherein said halobutyl rubberhas sidechains grafted thereto, wherein said sidechains are selectedfrom the group consisting of 3,4-polyisoprene rubber sidechains, highvinyl polybutadiene rubber sidechains, and medium vinyl polybutadienerubber sidechains.
 2. An elastomeric polymer as specified in claim 1wherein said sidechains are comprised of high vinyl polybutadiene.
 3. Anelastomeric polymer as specified in claim 1 wherein said sidechains arecomprised of medium vinyl polybutadiene.